In systems where a number of drives are coupled to one another by way of a strip, in particular a metal strip, e.g. in the case of a rolling system, or by way of a web, e.g. a paper web, speed adjustments to one drive are frequently passed on to the adjacent drives to minimize interference with the tension in the strip or web. This process is referred to as cascading. “Drives” here refer in particular to parts of the system driven by an electric motor with the associated regulation. Drives in a rolling system are for example roll stands, S-rolls (so-called bridles), reels, deflection rolls, etc.
There are fixed action directions during cascading. For example during rolling cascading preferably takes place in the direction of slower roll stands. A master drive or speed master drive is defined within the part of the system where the drives are being cascaded. Drives upstream of the master drive are cascaded in the action direction of the inlet, in other words counter to the production direction of the strip (upstream), while drives downstream of the master drive are cascaded in the action direct of the outlet (downstream), i.e. in the production direction.
In a multipart system, e.g. in a rolling system with a continuous annealing line CAL and a tandem cold mill TCR or a double cold reduction mill DCR as system parts, cascading causes the strip speeds of the system parts to change in relation to one another. A tandem train here refers to a roll stand arrangement, which is made up of at least two roll stands connected one behind the other in a production direction of the metal strip. In order to counteract the change in strip speed, which also affects the further system parts, loop accumulators are provided between the system parts. In a technologically tension-sensitive system arrangement such as a rolling system with a continuous annealing line and a downstream inline rolling mill in the form of a tandem cold mill, system-based decoupling by means of a loop accumulator is however generally not sufficient to transport the strip without interference through the continuous annealing line.
A rolling system for producing a metal strip is known from WO 2008/043605 A2, wherein a first roll stand of a tandem train is deployed with the function of a driver to achieve a build-up of mechanical tension in the metal strip and thus to dispense with a unit with a function that increases strip tension, e.g. an S-roll. As the function of the first roll stand is changed, the second roll stand in the production direction now represents the first actively rolling stand within the tandem train.